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12 TROUBLESHOOTING
MELSEC-ST
(2) Output circuit troubleshooting
The following explains possible problems in the output circuit and their corrective
actions.
Output circuit troubleshooting
Condition
Cause
Corrective
action
Example
1
When the
external
power
supply
turns on
the load
turns on
for a
moment
Erroneous output due to the stray capacitance (C) between
collector and emitter of photocoupler.
There is no erroneous output at normal load.
An erroneous output may occur at high sensitivity load
(such as solid state relay).
Base module
Output module
Constant
voltage
circuit
Photocoupler
Y0
24G
+24V
24V
SW
-
+
Shield
24G
C
Ic
Tr1
L
Connection from power
distribution module
If the external power supply is turned on precipitously, Ic
current flows due to the stray capacitance (C) between
collector and emitter of photocoupler.
When the current Ic flows, the potential difference is
generated between the source and gate of transistor Tr1,
which turns ON the output of Y0 for 100 s.
Approx.100 s
10ms or less
SW: External power
supply (24V)
at On
Output Y0
When external power supply turns
ON/OFF, check that the external power
supply rising edge must be 10ms or
more, and switch the SW1 to the
primary side of external power supply.
Primary side
External power
supply
SW1
PLC
Secondary side
When switching to the secondary side
of the external power supply is
required, the external power supply
rising edge connected a condenser
must be slow, and measured 10ms or
more.
Base module
Y0
24G
+24V
24V
SW
-
+
Shield
24G
C1
L
R1
Connection from power
distribution module
R1: Several tens of ohms
Power capacity
(external power current*
1
)
2
resistance value (3 to 5)*
2
C1: Several hundreds of microfarads
50V
*1 Refer to consumption current of the
external power supply for modules
used in this manual.
*2 Select the power capacity of
resistance to be 3 to 5 times lager
than the actual power consumption.
(Example)
R1 = 40 , C1=300 F
Use the below expression to
calculated a time constant
C1 R1 = 300 10
-6
40
= 12 10
-3
s
= 12ms
Summary of Contents for MELESEC-ST
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Page 23: ...A 21 A 21 MEMO...
Page 114: ...10 22 10 22 10 MOUNTING AND INSTALLATION MELSEC ST MEMO...
Page 125: ...11 11 11 11 11 EMC AND LOW VOLTAGE DIRECTIVE MELSEC ST MEMO...
Page 163: ...Index 2 Index 2 MEMO Ind...
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